How to achieve (automated) simultaneous outputs with Pipewire?

I'd like to have my system automatically output to all available sound devices (preferably using a sink in Pulseaudio Volume Control). This was possible when using Pulseaudio alone.

Is it possible with Pipewire? If yes, how would you achieve this?
Is it possible to set this up to be available automatically?

With PipeWire version 0.3.65, we have a native module available as well: module-combine-stream.

For the simultaneous output configuration, you'll want to use something like the following in pipewire.conf, adapted from the example in the documentation:

context.modules = [
{   name = libpipewire-module-combine-stream
    args = {
        combine.mode = sink
        node.name = "my_combined_sink"
        node.description = "My Combined Sink"
        combine.props = {
            audio.position = [ FL FR ]
        }
        stream.rules = [
            {
                matches = [
                    {
                        media.class = "Audio/Sink"
                    }
                ]
                actions = {
                    create-stream = {
                    }
                }
            }
        ]
    }
}
]

If you only want to combine specific sinks, you can of course add more entries to the matches array and specify node.name instead of matching all sinks.

If you don't know their names already, you can get all available sink names via pw-link -o.